The invention relates to a process for closing the evaporation chamber of an electrically heated steam iron having a sole member generally made of die-cast aluminium, an evaporation chamber fixedly connected to the sole member and closable by means of a lid, having a vertical steam chamber wall. The top surface of said evaporation chamber has rivets cast thereon with a substantially frustoconical base, and the lid has rivet holes associated with each rivet. The diameter of each rivet hole is equal to or larger than the diameter of the base of the rivet associated with the rivet hole and, after being placed on the top surface of the wall of the evaporation chamber the lid is attached to the sole member by deformation of the rivets.
In electric steam irons operating by the drip principle, the evaporation chamber in which water is converted from liquid form into vapor, and the associated steam channels, are provided in the electrically heated sole member. The water drips out of the water tank into the evaporation chamber. The wet steam thus produced is superheated in the steam channels and emerges on the ironing surface of the sole member. The sole member generally consists of die-cast aluminium. The evaporation chamber provided in the sole member, and the steam channels, are sealed off by means of a lid. As a result of the evaporation of the water and the physical processes which accompany this, pressure is generated in the evaporation chamber, acting all over the chamber walls.
The weakest point of the evaporation chamber is the point where the lid of the evaporation chamber joins the sole member which, is known steam irons, is produced by riveting. For this purpose, rivets having a substantially frustoconical base are cast on the top surface of the vertical steam chamber wall. The lid has rivet holes associated with each rivet. After the lid has been placed on the top surface of the steam chamber wall, the lid is fixedly connected to the sole member by deformation of the rivets. This known process has the disadvantage that the lid is connected to the sole member only by means of the deformed rivet heads. Since the rivets are cast on the steam chamber wall, it is absolutely necessary, for reasons of casting technology, for the base of each rivet to be frustoconical in shape. Moreover, owing to the tight joint between the lid and the evaporation chamber, before the riveting operation the lid must sit flush on the top surface of the steam chamber wall. This means that the cross-section of the rivet hole associated with each rivet in the cover must be equal to or larger than the maximum cross-section of the rivet base. As a result of the frustoconical rivet base, the volume of the rivet hole is not completely filled by the compressed rivet shank at the end of the riveting operation and the cross-section of the rivet head is only slightly bigger than the cross-section of the rivet hole. The rivet exerts no bearing pressure on the lid. As a result of the pressure acting on the lid from the evaporation chamber, the individual rivets are not subjected to tension, owing to the lack of bearing pressure. The pressure of the evaporation chamber acts solely as a shearing force on the rivet head. The lid is raised by the pressure of the evaporation chamber and the rivet heads are burst off by the shearing forces. As a result of the resulting leakage between the lid and the wall of the evaporation chamber, vapour and hence moisture penetrate into the interior of the iron. In the known steam irons, there is an exceptionally great danger that leakage currents will cause a short circuit or that a user will come into contact with the voltage of the appliance and suffer damage to his or her health.